1. Field of the Invention
The present invention relates generally to a photographic printer for producing three-dimensional (3D) photographs, and more specifically to a 3D printer which projects a set of 2D images onto a lenticular-type print material to form a composite 3D photograph.
2. Prior Art
In lenticular-type three-dimensional (3D) photography, the basic process involves taking a plurality of two-dimensional (2D) views from a number of horizontally-spaced vantage points and compressing these 2D views onto each of the lenticules on a lenticular screen to form a 3D composite image of the scene. It is understood that the above-mentioned lenticular screen typically is a sheet of transparent material with the front side embossed with an array of cylindrical lenses and the back side coated with photosensitive layers or the lenticular screen is attached to a photographic film or paper. Moreover, the 2D views typically are captured by a multi-lens camera and exposed in a number of frames on a photographic film. The basic process of producing a lenticular-type 3D photograph from a set of 2D frames has been discussed in detail in a number of books and patent disclosures. For example, Dudley discussed a printing method in "Applied Optics and Optical Engineering" (R. Kingslake, Ed., 1965) wherein the lenticular screen is transported intermittently so that each of the eight 2D images recorded on film is exposed at different angles. T. Okoshi, in "Three-Dimensional Imaging Techniques" (1978) discussed the use of several projectors to expose a plurality of 2D images onto the photographic emulsion. U.S. Pat. No. 3,482,913 of Glenn discloses a method of using a number of projectors for composing 3D photographs. U.S. Pat. No. 3,895,867 of Lo et al. discloses a technique of recording images on all of the film areas underlying the lenticules with intermittent exposure and shifting of the print material, U.S. Pat. No. 4,120,562 of Lo et al. discloses a scanning means for exposing a number of 2D images at different projection angles, and U.S. Pat. No. 4,101,210 of Lo et al. discloses a method of filling the film area underlying the lenticules by using a plurality of projection lenses.
When composing a 3D photograph, two basic procedures must be carried out to ensure a good result: 1) the selection of a "key-subject" on an image, and 2) the alignment of the key-subject in each view. The selection and alignment of the key-subject have also been discussed in a number of books and patent disclosures. N. A. Valyus, in "Stereoscopy" (Focal Press, 1966), discussed the importance of having proper registration of an image to obtain the 3D effect. In U.S. Pat. No. 3,895,867 of Lo et al a method is disclosed for printing in which each negative is visually examined to select an object which will become the center plane of the 3D picture. The selected object is known as the "key-subject". The key-subject in the photographed scene on each of the 2D views must be accurately registered on the lenticular print material in order to produce an in-focus 3D image, and this is one of the most important steps in producing lenticular-type 3D photographs. Because the relative location of the key-subject on each 2D negative varies with the distance of the key-subject from the camera, this location is likely to vary from one set of negatives to the next, or even from one set of 2-D images on the negative to the next set. Also, the key-subject is not necessarily in the center of the frame. Moreover, because the picture-taking lenses on a multi-lens 3D camera may not be perfectly identical or perfectly aligned on the camera, the relative locations are even more difficult to predict.
Key-subject alignment can be carried out manually by an operator or automatically by a computer or an electronic computing means when the 3-D photographs are cropped. Manual alignment methods have been mentioned in U.S. Pat. No. 4,903,069 of Lam and in U.S. Pat. No. 5,028,950 of Fritsch. In general, manual alignment of key-subject is time-consuming and relies heavily on the operator's skill and performance. In order to have a consistent quality and to increase the printing rate of a printer, it is desirable to implement an automated key-alignment scheme on a 3D printer.
Automated key-subject alignment methods have been mentioned or disclosed in a number of patent disclosures. U.S. Pat. No. 5,028,950 of Fritsch discloses key-subject alignment in a dual-stage 3D printer in which frame-to-frame registration data are produced electronically using a sophisticated image-processing system. In the disclosed dual-stage 3D printer, a first stage includes a CCD video camera with a 480.times.512 pixel array to capture the image on the negative and present it to the operator for key-subject designation. Within the same video image, an area of 28.times.28 pixels is used by an auto registration computer to conduct a correlation search on an image of 55.times.95 pixels (or larger area if necessary) from other frames in order to find the key-subject location. After the key-subject information is evaluated for all of the 2-D frames, the negative is transported to a second stage for printing. At the second (printing) stage the previously evaluated key-subject information is used to make adjustments in an effort to ensure registration. In theory, the relative location of the key-subject in each frame can be accurately computed in the first stage and, therefore, the key-subject can be accurately registered in the printing process (second stage). In practice, because such mechanical movement is not always accurate, errors in the registration of key-subject on the photograph do occur.
In the techniques disclosed in U.S. Pat. No. 5,028,950 of Fritsch discussed above, 2D negatives are exposed through a projection lens to form a 3D photograph, but the key-subject data are collected through a video camera. The video camera does not see the key-subject on the actual image that is exposed on the print material. For this reason, errors in key-subject alignment cannot be totally corrected, regardless of the computing algorithm used to find the relative locations of the key-subject. In particular, the printer disclosed in Fritsch uses two different mechanical stages for negative editing and for printing. The dimensional tolerances of such a complex mechanical design also can contribute to errors in key-subject registration.
Accordingly, it can be seen that a need yet remains for a 3-D photographic printer with key-subject alignment which provides consistent and accurate registration of the key-subject. It is to the provision of such a printer that the present invention is primarily directed.